Two very different types of models are consistent with most of the available facts in the fields of cognitive psychology and human information processing. One type of model characterizes mental processing as a series of sequential operations with discrete outputs, and the other characterizes mental processing as a series of cascading operations with continuous outputs. It is important to be able to discriminate between these two types of models, because they have very different implications about how researchers should design experiments to study mental processes. The goal of this research is to develop methods for discriminating between the two types of models. Several different experimental paradigms will be considered as possible means for distinguishing the models, and these paradigms will be applied across a wide range of stimuli and tasks. The main empirical question addressed by these experiments is whether preliminary information available to one mental process can be used by a succeeding mental process before the earlier one has finished. For example, can information about a partially recognized stimulus be used to start preparing responses before recognition of the entire stimulus is complete? Continuous models predict an affirmative answer, whereas discrete models predict a negative answer. While the answer need not be the same in all tasks, it is important to have methods capable of determining the answer for any particular task used in studies of mental processes.